Lidar Measurement Of Dust And Black Carbon Aerosols Over Lanzhou Areas

Atmospheric aerosol plays a significant role in regional and global climate change through its direct, indirect and semi-direct radiative effects. Lanzhou is a typical dust and smoke polluted city that located in northwest semi-arid region of China. Thus, it has important scientific meaning and application value to do long-term dust and smoke observations, their distribution and studies about their impacts to regional climate change.This paper used a relative long time dust storm observation data collected by CE370-2 in Lanzhou to analyze dust aerosol’s vertical distribution and transportation properties. We also used data from MAAP5012 and L2S-SM data to study Lanzhou’s black carbon mass concentration’s diurnal change, daily change,seasonal change and the vertical distribution of aerosol extinction coefficient and polarization. We got some quantitative results. Basing on these results, we can provide strong support to test simulation capability of the numerical model, adjust the parameters of the program and further improve the accuracy of model simulations.The main conclusions are listed below:(1) The analysis of a clear sky case study shows Lanzhou’s aerosol concentrate under 1.5 km in clear sky day. Lidar backscattering signal’s vertical cross sections profile is coincident with aerosol vertical profile. The whole day aerosol optical depths is small and the maximum value is 0.85. The diurnal change is not significant and the average aerosol optical depth is 0.42.(2) The analysis of aerosol vertical distribution to a dust storm from March 3-15, 2013 reveals that aerosol extinction coefficient has a good agreement with dust storm progress. Lidar’s detections heights are within 3km and dust aerosol concentrate under lkm. The aerosol optical depth is small before dust storm. The average aerosol optical depth before dust storm is about 0.8 and then the value increase rapidly to maximum 3.0. After dust storm is. AOD decreases from 9th to 13th. AOD changes in the pattern of small-big-small and finally deceased to 0.5, which is same as aerosol extinction coefficient change.(3) By analyzing the temperature and the relative humidity of the vertical profile in SACOL, Yuzhong, over the same period as above mentioned.There is an inversion layer at 500-1000m, the temperature decreasing with height above the inversion layer and in the lower layer where the temperature is 270K. Early dust, the maximum of relative humidity is above 40% in the lower layer, after the dust, the maximum relative humidity is 35% in the lower layer. We also found the trend of the vertical profile of relative humidity and the vertical profile of extinction coefficient quietly similar.(4) Using Multi-angle Absorption Photometer analysis the change ofconcentr-ation of black carbon in day and season. The results show that double peak structure of the concentration of black carbon in day, in 2009,2010 and the average between 2009 and 2010. The diurnal variation of the average is consistent with 2009 and 2010. The first peak occurs between 10:00 and 12:00, the highest value 3000ng/m3 in 2009, the second peak between 20:00 and 23:00 at night, the highest value 2900ng/m3 in 2010, the valley appeared around 18:00.(5) Contrast the daily change of concentration of black carbon between the station in city and the station in Yuzhong,the results show a double peak structure of the concentration of black carbon,but the city station is higher than that of Yuzhong station and the curve of city station changes in a higher fluctuations.The results even show that the concentration of lack carbon in heating period is higher than that in non-heating period.(6) Vertical distribution of aerosol extinction coefficients at 532 and 1064 nm and depolarization ratios at 532 nm, and the variation of aerosol optical depth (AOD) during the heating period are studied by using the observations from the L2S-SM Ⅱ polarization lidar. Aerosols mainly occur below 2 km in the distant rural area of Lanzhou. Large particles near the ground have larger extinction coefficients at 1064 nm than those at 532 nm. Polluted aerosols have depolarization ratios less than 0.2, while aerosols have depolarization ratios greater than 0.2 or more may be dust.(7) The average AOD during the heating periods of 2009,2010 and 2011 are 0.4, 0.32 and 1.1, about 60%,23% and 200% greater than that before the heating periods, separately. Aerosols are dominated by anthropogenic ones during the heating period in Lanzhou.